1. Field of the Invention
The present invention relates to a manufacturing method of an optical communication module, and particularly to a structure and a manufacturing method of the optical communication module, which couples an optical device to an optical fiber while preferably aligning them on a substrate.
2. Description of Related Art
An optical communication module couples an optical device such as a surface emitting laser and a photo-detector, which mutually convert an electrical signal and an optical signal via optical fiber. The optical communication module has attracted attention as a transmission means for communicating a large amount of information.
Conventionally, as for the optical coupling between an optical device and an optical fiber in a direction parallel to a substrate surface, for example, an optical device such as a surface emitting laser, as disclosed in Japanese laid-open patent application No. 14-296463, is mounted upright on a substrate, a V-shaped groove is formed on the substrate to hold an end part of the optical fiber, and the optical fiber is arranged so as to intersect a light-emitting surface or a light-receiving surface. For this arrangement, there has been used a method called visual alignment, in which the position of the V-shaped groove is monitored to align the optical device.
Furthermore, as a method for coupling an optical device and an optical fiber in a thickness direction of a substrate, as described in U.S. Pat. No. 5,904,545, for example, there has been proposed a technique, wherein the optical device is formed into a trapezoidal shape, a recessed part is provided at one surface of the substrate to fit the optical device thereto, and a through-hole penetrating up to the recessed part is formed on the other surface to insert the optical fiber thereto, so that an optical communication module is manufactured.
Structures of optical devices for receiving and transmitting an optical signal to be transmitted/received in a plane direction of a substrate are also disclosed in Japanese laid-open patent application No. 14-26440, and Japanese laid-open patent application No. 14-83953.
However, there have been various inconveniences in aligning an optical device and an optical fiber in the above-described related art. For example, in the technique disclosed in Patent Document 14-296463, a high-precision device is required for alignment and the alignment is performed one by one, which takes long time and entails an increase in manufacturing costs.
Furthermore, according to a method as disclosed in the above-described Patent Document U.S. Pat. No. 5,904,545, because the mounted trapezoidally-shaped optical device is supported at a bottom part of the recessed part to secure electrical coupling, there is a possibility that displacement occurs when the optical device is placed at the bottom part of the recessed part. In addition, because the step of forming the recessed part and the step of forming the through-hole are separate, there is no assurance that the through-hole is opened in such a manner that a central axis of the through-hole precisely coincides with a center of the recessed part. Therefore, even if the optical device happens to be placed precisely at the center of the recessed part, an optical axis of the optical fiber and a center of an emission optical axis of the optical device, which are inserted from the through-hole, do not surely coincide with each other. In the optical device such as a surface emitting laser, because a light-emitting point thereof is minute and the directivity of emitted light is strong, the optical fiber should be precisely brought into contact with the light-emitting region from a proper direction. Even a slight displacement of the optical fiber causes large light loss, which disables efficient optical communication.
Furthermore, although the optical devices described in the above-described Patent Documents 14-26440 and 14-83953 supports optical communication in plane directions, no concrete method for coupling optical fibers and the optical devices are provided.